Clad sheet alloys for brazing applications

ABSTRACT

This application discloses a multilayer aluminum material having an aluminum alloy core and an aluminum alloy cladding, wherein the aluminum alloy cladding contains ≦1.0 wt % Cu, ≦0.5 wt % Fe, ≦1.0 wt % Mn, ≦15 wt % Si, ≦0.15 wt % Ti, ≦7 wt % Zn and at least one of Sr or Na, remainder Al. The aluminum alloy cladding can also contain one or more of ≦0.2 wt % Mg or ≦0.05 wt % Ni. A process for producing the material is also disclosed. The material can be produced in sheet form and is suitable for brazing application. The metal forms fabricated from the multilayer aluminum material by a process comprising brazing steps are also disclosed.

RELATED APPLICATIONS

The present application claims the benefit of U.S. ProvisionalApplication Ser. No. 61/789,215, filed Mar. 15, 2013, which isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to the fields of material science,material chemistry, metallurgy, aluminum alloys, aluminum fabrication,and related fields.

BACKGROUND

Clad sheet alloys suitable for brazing applications comprise claddingproduced from commercial purity smelter aluminum, to which Si is added.Such conventional cladding aluminum alloys contain between 7 and 12% Si,<0.25% Fe and trace levels of other elements. Commercial purity smelteraluminum is more expensive than secondary or recycled aluminum. It isdesirable to decrease the costs of the clad sheet aluminum alloyssuitable for brazing applications by increasing the content of recycledaluminum alloys in such clad sheet alloys. It is also desirable toimprove the properties of the aluminum alloys suitable for brazingapplications, for example, in order to increase corrosion resistanceand/or strength of the brazing joints produced by brazing parts orobjects fabricated from clad sheet aluminum alloys.

SUMMARY

The terms “invention,” “the invention,” “this invention” and “thepresent invention” used herein are intended to refer broadly to all ofthe subject matter of this patent application and the claims below.Statements containing these terms should be understood not to limit thesubject matter described herein or to limit the meaning or scope of thepatent claims below. Covered embodiments of the invention are defined bythe claims, not this summary. This summary is a high-level overview ofvarious aspects of the invention and introduces some of the conceptsthat are further described in the Detailed Description section below.This summary is not intended to identify key or essential features ofthe claimed subject matter, nor is it intended to be used in isolationto determine the scope of the claimed subject matter. The subject mattershould be understood by reference to appropriate portions of the entirespecification, any or all drawings and each claim.

Aluminum alloys traditionally used for casting, rather than cladding,contain much higher levels of one or more of Fe, Cu, Mg, Mn, Ni, Si, Tior Zn than traditional cladding alloys. The inventor discovered thatsuch “casting alloys” can be used as cladding alloys in cast aluminumalloys suitable for brazing applications. The present invention providesa multilayer aluminum material comprising an aluminum alloy core andaluminum alloy cladding. This material, referred to as “clad aluminumalloy,” can be produced in sheet form and used for brazing applications.The present invention also provides processes for fabricating the abovealuminum materials, as well as the processes for fabricating metal formsand/or objects fabricated from the above aluminum materials. Alsoprovided are processes for using the above multilayer aluminummaterials, comprising joining by brazing metal forms or objects, atleast one of which is fabricated from the multilayer aluminum material.Brazing, as incorporated into the embodiments of the present invention,includes, but is not limited to, vacuum brazing, controlled atmospherebrazing, Borg-Warner Ni plating process or molten salt brazing.

One exemplary embodiment of the present invention is an aluminummaterial comprising an aluminum alloy core and an aluminum alloycladding, wherein the cladding comprises an aluminum alloy comprising≦1.0 wt % Cu, ≦0.5 wt % Fe, ≦1.5 wt % Mg, ≦1.0 wt % Mn, ≦2.5 wt % Ni,≦15 wt % Si, ≦0.15 wt % Ti, ≦7 wt % Zn and ≦0.05 wt % Sr. The materialcan be in a form of a sheet, comprising the cladding on one side of thesheet or on both sides of the sheet. Another exemplary embodiment of thepresent invention is a process for preparing the material of any one ofClaims 1 to 3, comprising: casting the cladding alloy; rolling thecladding alloy to a required thickness, thus producing the rolledcladding alloy; assembling the rolled cladding alloy onto at least oneside of a rolled core alloy; and hot roll bonding the rolled claddingalloy onto the rolled core alloy. Variations of the above processes cancomprise fusion casting by FUSION™ (Novelis, Atlanta, USA) process ofthe aluminum alloy core and the aluminum alloy cladding. The aboveprocesses can comprise, prior to casting, preparing the cladding alloyfrom scrap aluminum with addition of Si or from a combination of scrapaluminum and smelter grade aluminum. More generally, cladding aluminumalloy can contain recycled aluminum scrap metal. One more exemplaryembodiment of the present invention is a process comprising joining bybrazing at least one aluminum alloy form fabricated from a materialaccording to the embodiments of the present invention with a secondaluminum alloy form. Objects fabricated by a process comprising joiningby brazing are also included within the scope of the embodiments of thepresent invention. Some examples of such objects are a heater, anevaporator plate, an evaporator, a radiator, a heater core, a condenser,a tube, a pipe or a manifold.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a drawing schematically illustrating a clad-sheet aluminumalloy suitable for brazing.

FIG. 2 is a scheme illustrating an aluminum silicon phase diagram.

FIG. 3 is a reproduction of the electrochemical potential series.

FIG. 4 is a bar plot illustrating the results of a ThermoCalccalculation of melting temperatures of a range of aluminum alloys.

FIG. 5 is a scheme illustrating a generic casting/hot rolling processsuitable for production of sheet aluminum alloys. Reproduced withpermission from NSW HSC Online ©NSW Department of Education andCommunities, and Charles Sturt University, 2011.

FIG. 6 is photograph of an example of an oil cooler.

FIG. 7 is a photograph of an example of a radiator.

FIG. 8 is a photograph of an example of evaporator plates.

FIG. 9 is a photograph of an example of an evaporator.

FIG. 10 is a photograph showing rings of varying sizes, wires, coil ofwire and other shapes that can be used as filler during braze of notclad components.

FIG. 11 shows, in panel A, a schematic image of a cross-section of anexemplary multilayer aluminum sheet, and, in panel B, a schematic imageof a cross-section of a tube formed from a sheet of the kind shown inpanel A.

FIG. 12 is a micrograph illustrating a comparison of two experimentalcladding aluminum alloys in the “as cast” condition. Panel A shows alongitudinal section through an “as cast” ingot of a conventionalaluminum alloy AA4343+1% Zn modified with Sr. Panel B shows alongitudinal section through an “as cast” ingot of a cladding aluminumalloy according to an embodiment of the present invention.

FIG. 13 is a micrograph illustrating the comparison of the brazingsheets produced from each cladding alloy shown in FIG. 12. Panel A showsa longitudinal section of a clad sheet alloy in which conventionalaluminum alloy AA4343+1% Zn modified with Sr is clad onto one side ofX902 core alloy. Panel B shows a longitudinal section of variant 2cladding alloy clad onto X902 core alloy.

FIG. 14 is a micrograph showing post braze comparison of the samplesshown in FIG. 13.

FIG. 15 is a schematic image illustrating “Angle on Coupon” testing.

DETAILED DESCRIPTION

In this description, reference is made to alloys identified by AAnumbers and other related designations, such as “series.” For anunderstanding of the number designation system most commonly used innaming and identifying aluminum and its alloys, see “International AlloyDesignations and Chemical Composition Limits for Wrought Aluminum andWrought Aluminum Alloys” or “Registration Record of Aluminum AssociationAlloy Designations and Chemical Compositions Limits for Aluminum Alloysin the Form of Castings and Ingot,” both published by The AluminumAssociation.

Among other things, this document describes innovative multilayeraluminum materials comprising an aluminum alloy core and aluminum alloycladding. These multilayer aluminum materials can be referred to as“clad aluminum alloys.” The innovative multilayer aluminum materialsdescribed herein can be fabricated as sheets, with the cladding on oneor both sides of the sheet, in which case they can be referred to as“clad sheet aluminum alloys,” “clad aluminum sheets,” “clad sheetalloys” or by other related terms, in singular or plural. The term “cladaluminum alloy” and similar terms used herein are broader in scope thanthe term “clad sheet aluminum alloy” and similar terms. In other words,clad sheet aluminum alloys are a subset of clad aluminum alloys.

Clad aluminum alloys, including clad sheet aluminum alloys, can possessvarious compositions and properties. Some of these properties may beconferred by the chemical composition of the core and cladding layers,while other properties may be conferred by the manufacturing orfabrication processes used in the production or fabrication of cladaluminum alloys.

Clad sheet aluminum alloys described herein are suitable for fabricationor manufacturing processes that require the joining of metal surfaces bybrazing. Brazing is a metal joining process in which filler metal isheated above a melting point and distributed between two or moreclose-fitting parts by capillary action. In essence, when clad aluminumalloys described herein are used in a brazing process, the claddingmelts and becomes the filler metal that is available to flow bycapillary action to points of contact between the components beingbrazed. It is to be understood that it is not necessary for both or allparts being joined for brazing to be made of a clad sheet alloy. Atleast in some cases, it is sufficient for only one part of those partsbeing joined to be made of a clad sheet alloy. For example, a clad tubestock can be joined to a non-clad fin alloy in a radiator or anevaporator. In another example, a clad fin can be joined to a non-cladextrusion tube in a condenser. The uses of the clad sheet aluminumalloys in brazing and the related processes and results, such as theobjects fabricated according to the manufacturing process that involvebrazing, are generally referred to as “brazing applications.”

The inventor discovered that certain alloys traditionally used forcasting, rather than cladding, can be used as cladding alloys in cladaluminum alloys suitable for brazing applications. These traditional“casting alloys” contain much higher levels of one or more of Fe, Cu,Mg, Mn, Ni, Si, Ti, or Zn than cladding alloys conventionally used inbrazing applications. Use of these traditional “casting alloys” ascladding alloys in clad aluminum alloys for brazing applications resultsin a number of advantages discussed in more detail further in thisdocument. The inventor's discovery is embodied in the innovative cladaluminum alloys described herein, including clad sheet aluminum alloys,and in the processes related to the manufacturing and use of theseinnovative clad aluminum alloys. Some of the processes embodying theinventor's discovery are processes for fabricating or manufacturing ofthe innovative clad aluminum alloys. Some other processes embodying theinventor's discovery are processes for using clad aluminum alloys, whichinvolve brazing. The inventor's discovery is also embodied in the formsor objects that have brazed joints produced using the innovative cladaluminum alloys described herein.

Clad Aluminum Alloys

The innovative clad aluminum alloys according to the embodiments of thepresent invention differ from the conventional clad aluminum alloyssuitable for brazing applications in that the innovative clad aluminumalloys contain at least one cladding layer of an aluminum alloy thatcontains higher levels of one or more of Fe, Cu, Mg, Mn, Ni, Si, Ti, orZn than cladding alloys conventionally used in brazing applications. Theinnovative clad aluminum alloys described herein can be fabricated asclad sheet alloys that comprise core and cladding on one or both sidesof the sheet.

The terms “cladding,” “clad,” “cladding layer” and the related terms areused generally to refer to a relatively thin surface layer of amultilayer aluminum alloy. The terms “core,” “core layer” and therelated terms are used to refer to a relatively thicker layer of amultilayer aluminum alloy. A clad sheet aluminum alloy can have claddinglayers on both sides of the sheet, in which case a core layer is indeedan internal layer of the multilayer material. However, a clad sheetalloy can also have cladding on only one side of the sheet, in whichcase the core layer can also be on a surface. The core layer andcladding layer or layers typically have different chemical compositions.A clad sheet alloy can have two different cladding layers with differentcompositions and properties.

It is to be understood that clad aluminum alloys suitable for brazingapplications do not necessarily contain only a core layer and one or twocladding layers. Clad aluminum alloys can contain other layers, some ofwhich may be referred to as “interlayers,” “outer layers,” “liners” andby other related terms. This concept is illustrated in some examplesdiscussed and shown elsewhere in this document. Some examples of cladaluminum alloys are illustrated in FIGS. 1 and 11. Clad sheet aluminumalloys can have 2, 3, 4, 5, 6 or more distinct layers, each having acertain function. More generally, a clad sheet aluminum alloy can haveas many layers as can be stacked and bonded together in one or moreoperations. In the commercial context, one possible limiting factor isthe cost of production and/or scrap generated during production ofmultilayer alloys, which can become too high with the increased numberof layers for the multilayer alloy to be commercially viable. In thecontext of clad sheet aluminum alloys suitable for brazing applications,one or more of the cladding layers are the portion of the sheet thatmelt during a braze cycle. A liner can be a layer that is not expectedto melt during a braze cycle and may confer some other benefits, such ascorrosion resistance or increased strength, onto the multilayer aluminumalloy. A core can also include multiple layers, such as one or moreinterlayers on one or both side of the main core layer.

The composition of the cladding suitable for brazing applications, whichcan be termed “brazing aluminum alloy,” “brazing cladding alloy,”“cladding alloy for brazing” and other related terms is illustrated inTable 1. The content of the elements listed in Table 1 can fall withinthe ranges delimited by a lower range limit and an upper range limitshown in Table 1. A lower range limit can be delineated by expressions“equal to or more than” (≧sign) or “more than” (>sign), or other relatedsigns and expression, such as “from . . . ,” “higher than” etc. An upperrange limits can be delineated by expressions “equal to or less than”(≦sign), “less than” (<sign) or other related signs and expressions,such as “to,” “less than,” etc. Other types of expressions can also beused to delineate the ranges, such as “between,” “in the range of,” etc.When a range is delineated by only the upper range limit, it is to beunderstood that, in some examples falling within such a range, anelement in question may not be present, may not be present in detectablequantities, or may be present in such low quantities that they areconventionally not recognized as meaningful in the field of aluminumalloys. It is to be understood that the term “remainder” can be used todescribe aluminum (Al) content in the aluminum alloys. It is also to beunderstood that some other additives and/or elements can be present inthe aluminum alloy, which are not necessarily listed in Table 1. A wideselection of possible cladding alloys are documented in a documentpublished by The Aluminum Association, namely, “Registration Record ofAluminum Association Alloy Designations and Chemical Compositions in theForm of Castings and Ingot”.

The presence and the content of one or more elements included in Table1, as well as some other elements not necessarily listed in Table 1, canaffect properties of the cladding aluminum alloy according to thegeneral principles known in the field of metallurgy and brieflysummarized below. It is therefore possible to change the properties ofthe cladding layer and the clad aluminum alloy that incorporates thecladding layer by varying the presence and the content of one or more ofthe elements, some of which are discussed below.

Cu: Cu in solid solution increases strength of an aluminum alloy.Depending on concentration, Cu can have an effect on corrosionresistance of an aluminum alloy. For example, in the clad aluminumalloys according to some embodiments of the present invention, Cu insolid solution can increase the corrosion resistance by lowering thespread between the corrosion potential (ASTM G69 SCE) of the matrix andthe Si particles in the eutectic system.

Fe: Relatively small amounts of Fe may be present in solid solution inan aluminum alloy after processing. Fe can be a part of intermetallicconstituents which may contain Mn, Si, and other elements. It is oftenbeneficial to control Fe content in an aluminum alloy to avoid largeconstituents, which do not contribute to the beneficial properties ofthe alloy, such as fracture toughness. In conventional cladding alloys,Fe content is kept low to avoid formation of Beta AlFeSi which is inneedle form. The aluminum alloys used for the cladding layer in theembodiments of the present invention can tolerate higher thanconventionally acceptable levels of Fe.

TABLE 1 Composition of cladding alloy for brazing (element content in wt%) Examples of Examples of upper Range examples Element lower rangelimit range limit Range 1 Range 2 Range 3 Cu 0.05; 0.1; 0.15; 0.2 0.3;0.35; 0.4; ≦1.0 ≦0.6 0.2-0.3 0.45; 0.5; 0.55; 0.6; 0.65; 0.7; 0.75; 0.8;0.85; 0.9; 0.95; 1.0 Fe 0.05; 0.1; 0.15; 0.2 0.3; 0.35; 0.4; ≦0.5 ≦0.30.2-0.3 0.45; 0.5 Mg 0.05; 0.1; 0.2; 0.3;; ≦0.1 ≦0.5 ≦1.5 0.4; 0.5; 0.6;0.7; 0.8; 0.9; 1.0; 1.1; 1.2; 1.3; 1.4; 1.5 Mn 0.6; 0.65; 0.7; ≦1 ≦0.75≦0.6 0.75; 0.8; 0.85; 0.9; 0.95; 1 Ni 0.05; 0.1; 0.2; 0.3; ≦2.5 ≦0.5≦0.05 0.4; 0.5; 0.6; 0.7; 0.8; 0.9; 1; 1; 1.0; 1.1; 1.2; 1.3; 1.4; 1.5;1.6; 1.7; 1.8; 1.9; 2; 2.1; 2.2; 2.3; 2.4; 2.5 Si 3; 4; 5; 6; 7 12; 13;14; 15 ≦15  3-12  7-12 Ti 0.01; 0.02; 0.03; 0.04; 0.1; 0.15 ≦0.150.01-0.15 0.05-0.15 0.05 Zn 3.5; 4; 4.5; 5; 5.5; ≦7 ≦5 ≦3.5 6; 6.5; 7 Sr0.005; 0.01 0.025; 0.03; 0.035; ≦0.05 ≦0.03 0.01-0.025 0.04; 0.045; 0.05

Mg: Mg is generally added for strength in aluminum alloys. In brazingapplications, Mg can be added to improve vacuum brazing in that it helpsto break up the surface oxide, so that filler metal can wet adjacentsurfaces. It is, however, detrimental to controlled atmosphere brazing(CAB), where Mg reacts with the flux to create solid needles of KMgF₂during the brazing cycle. To be suitable for CAB brazing, cladding alloytypically needs to contain ≦0.2 wt % Mg, unless special fluxes are usedto limit or eliminate the formation of the KMgF₂ needles. To be suitablefor vacuum brazing, cladding alloy typically needs to contain fromapproximately 0.2 to 1.5 wt % Mg, To be suitable for Borg-Warnerprocess, cladding alloy typically needs to contain up to approximately0.5 wt % Mg,

Mn: Mn in solid solution increases strength of an aluminum alloy andmoves corrosion potential towards a more cathodic state. (FeMn)—Al₆ orAl₁₅Mn₃Si₂ dispersoid increases strength of an aluminum alloy byparticle strengthening, when present in a fine and dense dispersion. Mnpresent in the cladding alloys used in the embodiments of the presentinvention may promote the formation of the Cubic Alpha AlFeMnSi phase,which is blocky or acicular in shape. Depending on the composition andsolidification rate, Fe, Mn, Al and Si combine during solidification toform various intermetallic constituents, i.e. particles within themicrostructure, like Al₁₅(FeMn)₃Si₂ or Al₅FeSi or Al₈FeMg₃Si₆, to name afew.

Ni: Ni forms NiAl₃, which is highly cathodic in aluminum alloys. Ni insolid solution promotes corrosion when present at levels above 100 ppmin an aluminum alloy. In some embodiments of the present invention, itis therefore beneficial to have low Ni levels in the cladding alloy.Notwithstanding the composition limits shown in Table 1, it isunderstood that Ni content can be higher in post braze materialsproduced through the Borg-Warner process or in applications that wouldnot involve corrosive environments where the presence of NiAl₃ would bedetrimental.

Si: Si is used at different concentration to allow for a multitude ofmelting ranges necessary for different brazing applications, asillustrated by aluminum silicon phase diagram shown in FIG. 2.

Ti: Ti can improve corrosion resistance when present in 0.1-0.22 wt %range in an aluminum alloy. As a peritectic element, Ti is concentratedin the center of the cells after alloy re-solidification.

Zn: Zn is typically added to aluminum alloys to move the corrosionpotential towards the anodic end of the scale, as illustrated byElectrochemical Potential Series shown in FIG. 3. Zn can be astrengthening element, when elements such as Cu, Mg are present, such asin 7000 series alloys. For example, wrought Al 7000 contains between 3.0to 9.7% Zn; 700 series casting alloys contain between 2.7 and 8% Zn.

Sr or Na: Sr or Na is generally added to AlSi alloys to modify the Siparticles from needle-shaped to fine spherical. Sr and Na metals aremost beneficial during direct chill casting, where solidification ratesare relatively slow. Sr remains longer in the molten Al and thus allowsfor more time before casting takes place, while Na starts to evaporatefaster from the molten metal so restricts the time before casting. BothSr and Na are effective at modifying the Si in AlSi alloys.

In one example, a cladding aluminum alloy contains ≦1.0 wt % Cu, ≦0.5 wt% Fe, ≦1.5 wt % Mg, ≦1.0 wt % Mn, ≦2.5 wt % Ni, ≦15 wt % Si, ≦0.15 wt %Ti, ≦7 wt % Zn and ≦0.05 wt % Sr. In one more example, a claddingaluminum alloy contains ≦1.0 wt % Cu, ≦0.5 wt % Fe, ≦0.2 wt % Mg, ≦1.0wt % Mn, ≦0.05 wt % Ni, ≦15 wt % Si, ≦0.15 wt % Ti, ≦7 wt % Zn and ≦0.05wt % Sr. In another example, a cladding aluminum alloy contains 0.2-0.3wt % Cu, 0.2-0.3 wt % Fe, ≦0.1 wt % Mg,; ≦0.6 wt % Mn, 0.005-0.02 wt %Ni, 7-12 wt % Si, 0.05-0.15 wt % Ti, 0-3.5 wt % Zn and 0.01-0.025 wt %Sr.

Clad aluminum alloys described herein contain a core aluminum alloy.Examples of core aluminum alloys are described, for example, in U.S.Pat. No. 4,649,087. A core aluminum alloy can be any 3xxx or 6xxx seriesalloy that can be brazed without undue melting or dissolution due to itsinherent melting range. Core aluminum alloys can be the alloys commonlydescribed as “Long Life,” meaning that they use a mechanism to slow downthe corrosion through the core. One example of such mechanism isdescribed in U.S. Pat. Nos. 5,041,343 and 5,037,707. As discussed inthese patents, a dense precipitate band forms during the braze cycle inthe core adjacent to the interface between the core alloy and thecladding alloy. This dense precipitate band is sacrificial to the coreduring corrosion, resulting in slowing down of the corrosion of thecore.

Properties and Advantages

Conventionally, the cladding in the clad aluminum alloys used forbrazing applications is produced from commercial purity smelteraluminum, to which Si is added. Conventional brazing cladding typicallycontains between 7 and 12% Si and <0.25% Fe. Mg can be present if thealloy is to be used in vacuum brazing applications. Other elements aretypically present in such conventional cladding alloys at trace levels,such as <0.05 wt % or less than 0.005 wt %. Commercial purity smeltermetal, which is required for production of the above conventionalcladding alloys due to their high purity, is more expensive thansecondary or recycled metal.

Wrought aluminum alloys are not used as cladding alloys for brazingapplications because they are possibly considered to be inferior inquality and consistency. Generally, a limited number of brazing claddingalloys is traditionally used in the field of aluminum metallurgy and inthe related fields. For example, for inert atmosphere brazing, alloyslike AA4343, 4045 and 4047 are the mostly commonly used cladding alloys.Conventional brazing cladding alloys have a relatively well known anddefined melting range, as they primarily include Al, Si and possibly Znor Mg. The phase diagrams determined the choice of the alloys suitablefor brazing in the aluminum industry. Refer, for example, to“Multicomponent Phase Diagrams: Applications for Commercial AluminumAlloys” Elsevier, 2005, ISBN 0-080-44537-3.

Surprisingly, the inventor discovered that wrought aluminum alloys canbe advantageously recycled and used as a cladding alloy in clad aluminumalloys for brazing applications. Wrought aluminum alloys can also beadvantageously combined with conventional high purity smelter metal andused as cladding alloy in clad aluminum alloys for brazing applications.Thus, the embodiments of the present invention incorporate a claddingalloy that can be derived from a mixture of smelter grade aluminum withthe addition of various clean aluminum alloy scrap. A brazing claddingalloy incorporated into the embodiments of the present invention canalso be produced from clean scrap aluminum, to which Si is added toproduce an alloy with the desired melting range. The cladding alloysdescribed herein have one or more other advantages over conventionalcladding alloys, particularly when used in fabricating sheet materialsfor brazing-compatible applications.

The present invention allows for recycling of wrought aluminum thatcommercial rolling and casting facilities produce. The term “recycling”and related terms are used herein to describe a notion that previouslyfabricated aluminum alloys or objects prepared from such alloys can becombined and treated by metallurgical processes to fabricatecommercially and technologically useful aluminum alloys, which can becharacterized as “recycled.” Cladding brazing alloys incorporated intothe embodiments of the present invention can contain up to 100% orrecycled aluminum, or “scrap.” In some cases, the only additionalelement to be added to scrap aluminum to produce the recycled claddingalloys is Si in order to achieve Si content required for the desiredmelting range, such as 7.5% Si or 10% Si. Experimentation according tothe procedures known in the field of metallurgy can be conducted todetermine the levels of the elements other than Al that can be suitablefor various brazing applications.

Using recycled wrought aluminum as a component of cladding alloys canreduce the cost of the innovative clad sheet aluminum alloys for brazingapplications. The following example is included to illustrate thispoint. If a price of $1,500 per ton is set for smelter grade aluminum,then scrap aluminum is likely to sell for approximately half of theabove price. When clad sheet aluminum alloys are made commercially,scrap is generated by trimming and discarding various portions of aningot, hot rolled slab, or cold rolled material. This scrap, afterre-melting, is a mixture of both cladding and core. If the cladding isfabricated from smelter grade aluminum plus Si, and the core is a highMn, Cu alloy, then the scrap has a composition somewhere in between thecladding and the core alloys, depending on the overall original claddingthickness and at what point in the processing the material was scrapped.The cladding alloys employed in the clad aluminum alloys according tothe embodiments of the present invention can be prepared from such scrapafter the addition of Si, with the resulting price in the abovehypothetical situation being lower than the smelter grade aluminum (forexample, approximately 10, 20, 30, or 40% lower).

An advantage of the cladding alloys incorporated into the embodiments ofthe present invention is that the fillets or residual cladding producedpost-brazing can resist corrosion better than the fillets or theresidual cladding produced by conventional cladding alloys. The improvedcorrosion resistance is due to the presence of additional elements inthe cladding alloys used in the clad aluminum alloys of the presentinvention, in comparison to conventional cladding alloys. Two examplesof such additional elements that can beneficially affect the corrosionproperties of the fillets and the residual cladding, which can act asprotective anti-corrosion coating in the parts and objects subjected tobrazing, are Cu and Mn. Cu and/or Mn, when present in solid solution inan aluminum alloy, raise the corrosion potential of alpha Al. Thisreduces the spread between the Si particles, which are very cathodic,and alpha Al. The increased corrosion resistance is based on the knownprinciples, some of which are illustrated in the corrosion diagramreproduced in FIG. 3. For example, if one considers that relatively pureSi has ASTM G69 open coupled corrosion potential (sce) of −170 mv, andalpha Al without Cu has open coupled corrosion potential in the range−760 to −740 mv, then adding 0.1 wt %. Cu to the Alpha Al would make itmore cathodic by about 50 mv. Adding 1 wt % Mn to alpha Al would movethe corrosion potential further in the cathodic direction, thus closingthe gap between the matrix and the Si particles. Elements other than Mgcan move the potential even further when present in the cladding alloy,in accordance with the known electrochemical principles.

The improved cladding alloys incorporated into the clad sheet aluminumalloys described herein are stronger than conventional cladding alloysdue to the presence of one or more of the metals in addition toaluminum, as illustrated in Table 1. One or more additional elements canbe present in solid solution and/or in constituent form. Two examples ofsuch additional elements that affect the strength of the fillets are Cuand Mn. Common brazing cladding alloys, which are made fromsubstantially pure Al with addition to Si, are relatively soft incomparison to the cladding alloys incorporated into the embodiments ofthe present invention. Table 2 shows tensile properties of a selectionof conventional cladding aluminum alloys and of exemplary castingaluminum alloys, thus illustrating the compositions and properties thatcan be advantageously incorporated into embodiments of the presentinvention.

The increased strength of the cladding alloys incorporated in theembodiments of the present invention minimizes the loss of cladding bysqueeze out on the edges of packages during the rolling processestypically employed in the fabrication of clad sheet alloys. Claddingalloys used in the embodiments of the present invention also resistspreading during hot rolling and allow for larger reductions per pass,which, in some cases, helps to reduce the spread in cladding thicknessbetween edge and center, a common disadvantage of conventional cladsheet alloys. The cladding alloys incorporated into the clad sheetalloys according to the embodiments of the present invention can ensuremore consistent cladding thickness across the width of the clad sheet.

The strength data on 4343 and 4045 alloys shown in Table 2 wasexperimentally obtained. Other strength data shown in Table 2 wereobtained from MatWeb material property data website in the non-ferroussection under aluminum alloys. The strengths of casting alloys shown inTable 2 were measured at room temperature. When subjected to highertemperatures, Al alloys become softer. As an example AA1100 tested atroom temperature has ultimate tensile strength (UTS) of 90 MPa, whileAA1100 tested at 371° C. has UTS of 14.5 MPa. AA3003 has UTS ofapproximately 110 MPa at room temperature, but UTS of 19 MPa at 371° C.It is therefore to be understood that Table 2 serves as illustration ofroom temperature strength properties of cladding aluminum alloys.Strength properties, such as UTS, can be reduced by as much as 85-95% athot rolling temperatures, in comparison to the same properties measuredat room temperature. The tensile data at different temperature is shownin the materials published by the Aluminum Association, namely, AluminumStandards and Data 1997, for example, pages 2-5, 2-7 and 2-9.

Yet one more advantage of the cladding aluminum alloys incorporated intothe clad aluminum alloys described herein is that they can melt at lowertemperature during a brazing or similar process, as compared toconventional brazing cladding. This offers a cost benefit in themanufacture of brazed components and/or parts due, for example, toreduced energy expenditures. To illustrate reduced melting temperatures,Table 3 and the bar graph shown in FIG. 4 were generated by ThermoCalcsoftware (Thermo-Calc Software, Inc, McMurray Pa.) and show thataluminum alloys containing additional elements melt at significantlyreduced temperature than aluminum alloys with similar Si content butlower levels of one or more additional elements. For example alloy 4343at 7 wt % of Si melts in a temperature range from 573.5° C. (solidus,meaning the temperature at which the metal starts to melt) to 612.8° C.(liquidus, meaning the temperature at which the material is fullymolten). In comparison, a casting alloy, such as A356 containing asimilar level of Si, melts in a temperature range from 550° C. (solidus)to 607° C. (liquidus).

The following examples are included to illustrate the properties andadvantages discussed above. In one example, tube stock for radiators iscommonly composed of a core alloy which is clad between 3% and 18% inrelation to full thickness on one side with an Al—Si alloy (AA4343,AA4045+/−Zn) and possibly also with a liner alloy on the opposite side.In another example, evaporator plates can be made from AA4343 alloy eachclad 5% to 15% on both sides of a core alloy. Both of the above cladalloys can be advantageously produced with the cladding describedherein. Generally, the requirements for cladding alloy is to melt andflow at the manufacturer's required brazing temperature and to offer acertain required strength post braze, so that the brazed part or objectcan withstand various testing conditions demonstrating compliance withthe service requirements, such as burst pressure, cyclic fatigue,corrosion resistance, etc. Having a brazing alloy that can melt and flowat a lower temperature lowers the costs of brazing processes, as theycan be conducted at lower brazing temperatures. A stronger and lesscorrosion-prone cladding alloy can advantageously improve the propertiesof the objects fabricated from such an alloy, such as a radiator or anevaporator.

TABLE 2 Tensile properties of exemplary aluminum alloys. Mn Ni Zn Ti YS*UTS** Alloy Si wt % Cu wt % Fe wt % Mg wt % wt % wt % wt % wt % (MPa)(MPa) 4043-0 4.5-6.0 Trace Trace Trace Trace Trace Trace Trace 70 1454343 7.0-8.0 Trace Trace Trace Trace Trace Trace Trace 4045 - O 10 TraceTrace Trace Trace Trace Trace Trace 57 115 4047 12 Trace Trace TraceTrace Trace Trace Trace 65 140 A413.0-F 11-13 ≦1.0 ≦1.30 ≦0.10 ≦0.35≦0.15 ≦0.50 ≦0.050 131 290 A356 6.50-7.50 ≦0.20 ≦0.15 0.30-0.45 ≦0.10≦0.050 ≦0.10 0.20 131-145 A360.0-F  9.0-10.0 ≦0.60 ≦2.0 0.40-0.60 ≦0.35≦0.50 ≦0.50 ≦0.050 170 300 *YS = yield strength; **UTS = ultimatetensile strength

TABLE 3 Calculated melting range for various aluminum alloys ALLOY 40434343 4047 A413.0-F A356 A360.0-F Si and Mg 4.5 Si 6 Si 7 Si 8 Si 11 Si13 Si 6.5 Si 7.5 Si 9 Si Variant 1* Variant 2* Variant 3* 10 Si levels0.3 Mg 0.45 Mg 0.4 Mg 0.6 Mg (wt %) Liquidus 904.2 893.3 885.8 878.1847.1 856.6 888.7 880.4 863.8 879.9 876.1 875.5 854.9 (K) Liquidus 631.2620.3 612.8 605.1 574.1 583.6 615.7 607.4 590.8 606.9 603.1 602.5 581.9(° C.) Solidus 846.5 846.5 846.5 846.5 846.5 815.2 826.9 823.3 817.7836.9 832.1 830.7 818.8 (K) Solidus 573.5 573.5 573.5 573.5 573.5 572.2553.9 550.3 544.7 563.9 559.1 557.7 545.8 (° C.) *Please refer to Table4 for compositions of “Variant 1,” “Variant 3” and “Variant 4” of A356alloy

Processes

The processes for making or fabricating the clad aluminum alloysdescribed herein, as well as for fabricating the objects using the cladaluminum alloys are also included within the scope of the presentinvention. One exemplary process is schematically illustrated in FIG. 5.Clad aluminum described herein can be fabricated by the processes thatinclude at least some of the technological steps described and shown inthis document. It is to be understood that descriptions andillustrations of the processes contained in this document arenon-limiting. The process steps described herein can be combined andmodified in various ways and suitably employed for fabricating the cladaluminum alloys or forms and objects from such alloys. Process steps andconditions that are not explicitly described herein, yet commonlyemployed in the areas of metallurgy and aluminum processing andfabrication, can also be incorporated into the processes falling withinthe scope of the present invention.

One technology that can be suitably incorporated into the processesaccording to the embodiments of the present invention is “fusioncasting,” which can be also referred to by the trade name FUSION™(Novelis, Atlanta, US), and is described, for example, in U.S. Pat. No.7,472.740. Generally, fusion casting is a process of casting of acomposite or multilayer metal ingot. When casting by the FUSION™(Novelis, Atlanta, US) process is employed for production of the castaluminum alloy described herein, a cladding alloy is solidified on oneor both surfaces of a partially solidified core alloy. A fusion castingprocess typically uses a mold with a feed end and an exit end. Themolten metal is added at the feed end, and a solidified ingot isextracted from the exit end of the mold. Divider walls are used todivide the feed end into at least two separate feed chambers. Thedivider walls terminate above the exit end of the mold. Each feedchamber is adjacent to at least one other feed chamber. For each pair ofadjacent feed chambers, a stream of a first alloy is fed to one of thepair of chambers to form a pool of metal in the first chamber. A streamof a second alloy is fed through the second of the pair of feed chambersto form a pool of metal in the second chamber. The first metal poolcontacts the divider wall between the pair of chambers to cool the firstpool, so as to form a self-supporting surface adjacent the divider wall.The second metal pool is then brought into contact with the first pool,so that the second pool first contacts the self-supporting surface ofthe first pool at a point where the temperature of the self-supportingsurface is below the solidus temperature of the first alloy. The twoalloy pools are joined as two layers and cooled to form a composite ormultilayer ingot, which can be also referred to as “package.” Themultilayer ingot obtained by fusion casting is included within the scopeof the clad aluminum alloys described herein.

It is to be understood that multilayer aluminum alloys can be producedby the processes other than fusion casting. For example, the claddingalloy can be cast by continuous (C.C.) or direct chill (D.C.) casting,hot-rolled to a required thickness, and then assembled or clad onto oneor both sides of a core alloy by hot roll bonding. Thus produced “hotrolled band” can be cold rolled to an intermediate gauge and annealed orcold rolled in a number of passes to a final gauge.

Hot rolling can be suitably incorporated into the processes according tothe embodiments of the present invention. For example, packages oringots, produced by the direct chill or FUSION™ (Novelis, Atlanta, US)process, are reheated to a temperature between 450° C. and 550° C. andhot rolled to an intermediate gauge of 2 to 10 mm. Reheating can takeplace in a pusher furnace over a 5 to 10 h period or in a pit furnaceover a 15 to 24 h period. The pre-heating process can be optionallyincorporated into the process of the present invention.

Cold rolling can also be suitably incorporated into the processesaccording to the embodiments of the present invention. Depending on thehot rolling final gauge, a cast aluminum alloy may require more or fewercold rolling passes. For example, cold rolling can involve 1 to 6 coldrolling passes, depending on the hot band gauge supplied from the hotmill. This number of cold passes is not limited and can be suitablyadjusted, for example, depending on the desirable thickness of the finalsheet. A thickness achieved by cold rolling can be from 50 microns to 1mm. Some examples of thicknesses achieved by cold rolling are 50 microns(typically used for fin materials) and 200 microns, and 1 mm for tubestock components.

Annealing can also be incorporated into the processes according to theembodiments of the present invention. For example, a clad sheet aluminumalloy can be partially or fully annealed to achieve suitable formabilityrequirements.

Clad sheet aluminum alloys are suitable for brazing applications.Accordingly, various brazing processes and technological steps can besuitably employed in the embodiments of the present invention. Brazingof aluminum parts is generally described in U.S. Pat. No. 3,970,327.Brazing includes salt brazing, CAB brazing, vacuum brazing and Ni-platedbrazing. Brazing of a clad sheet aluminum alloy requires a claddingalloy that melts at a temperature significantly lower than the corealloy. Standard commercial Al—Si cladding alloys used for brazingapplications usually start to melt at about 575° C.-577° C. and arefully liquid at the temperatures between 577° C. and 615° C., dependingon the Si content. The core typically melts at 645° C. and above. Theclad aluminum alloys of the present invention behave in accordance withthe above requirements.

Furthermore, because of the additional elements present in the claddinglayer, clad aluminum alloys described herein may advantageously have alower melting point of the cladding than conventional clad aluminumalloys used for brazing applications. For example, ThermoCalcsimulations showed that the cladding incorporated into the clad sheetalloys of the present invention can melt at a significantly lowertemperature than conventional aluminum alloys of the same Si content.

In one exemplary process, two forms fabricated from a clad sheetaluminum alloy are assembled, secured, optionally fluxed, if brazing isto be carried out in an inert atmosphere, and then brazed. Brazingprocess can be a vacuum brazing process if the core and the cladding ofthe clad sheet aluminum alloy contain suitable levels of Mg, usuallyfrom 0.25% to 1.5% by weight of Mg. For example, brazing can beconducted at a temperature of 600° C.-605° C.

Uses and Applications

Uses and applications of the clad aluminum alloys described herein areincluded within the scope of the present invention, as are objects,forms, apparatuses and similar things fabricated with or comprising theclad aluminum alloys described herein. The processes for fabricating,producing or manufacturing such objects, forms, apparatuses and similarthings are also included within the scope of the present invention.

One exemplary object is a heat exchanger. Heat exchangers are producedby the assembly of parts comprising tubes, plates, fins, headers, andside supports to name a few. For example, a radiator is built fromtubes, fins, headers and side supports. Except for the fins, which aretypically bare, meaning not clad with a Al—Si alloy, all other parts ofa heat exchanger are typically clad with a brazing cladding on one ortwo sides. Once assembled, a heat exchanger unit is secured by bandingor such device to hold the unit together through fluxing and brazing.Brazing is commonly effected by passing the unit through a tunnelfurnace. Brazing can also be performed by dipping in molten salt or in abatch or semi-batch process. The unit is heated to a brazing temperaturebetween 590° C. and 610° C., soaked at an appropriate temperature untiljoints are created by capillary action and then cooled below the solidusof the filler metal. Heating rate is dependent on the furnace type andthe size of the heat exchanger produced.

Some other exemplary objects that can be made with the alloys of thepresent invention are described and shown in U.S. Pat. No. 8,349,470.Some examples of such objects are an evaporator plate, an evaporator, aradiator, a heater, a heater core, a condenser, condenser tubes, varioustubes and pipes, a manifold, and some structural features, such as sidesupports. The uses of the cladding brazing aluminum alloys according tothe present invention are not limited to the processes that involvebrazing cladding alloys onto core alloys or interlayer alloys. Forexample, cladding brazing aluminum alloys can be produced for fillerrings made from drawn wire. In another example, a cladding brazingaluminum alloy produced in sheet form can be used as filler shim. Theshim material can have a thickness anywhere from a few microns to amillimeter, depending on the application. Some of the above embodimentsare illustrated in FIGS. 6-11.

The following examples will serve to further illustrate the presentinvention without, at the same time, however, constituting anylimitation thereof. On the contrary, it is to be clearly understood thatresort may be had to various embodiments, modifications and equivalentsthereof which, after reading the description herein, may suggestthemselves to those skilled in the art without departing from the spiritof the invention. During the studies described in the followingexamples, conventional procedures were followed, unless otherwisestated. Some of the procedures are described below for illustrativepurposes.

EXAMPLE 1

Three variants of a casting alloy similar to A356 were produced and cladon X902 or X912 cores. X902 is an alloy containing nominal 1.4-1.6 Mn,0.5-0.65 Cu, ≦0.15 Si, ≦0.02 Mg, ≦0.015 Ti, all in wt %. X912 is analloy having X902 base with 0.1 wt % Ti addition. Four conventionalcladding alloys of 4343 series clad on X902 and X912 core were used ascontrols. Clad sheet alloys were processed to 0.3 and 0.25 mm and thenexposed to a braze cycle to confirm the cladding alloys would melt andflow. ThermoCalc analysis was performed to check melting range and typesof constituents. The alloys tested are characterized in Tables 3 and 4.

TABLE 4 Composition of the cladding alloys (wt %). ALLOY Cu Fe Mg Mn NiSi Ti Zn Sr 4343 1 Zn 0.0016 0.18 0.0008 0.0034 0.0083 7.34 0.0075 0.970.0139 4343 2 Zn 0.0015 0.19 0.0008 0.0033 0.0087 7.39 0.0076 2.080.0138 4343 5 Zn 0.0016 0.22 0.0009 0.0036 0.0095 7.35 0.0072 5.010.0132 4343 7 Zn 0.0017 0.23 0.0009 0.0038 0.0101 7.17 0.0071 6.930.0119 ~A356 0.22 0.20 0.075 0.35 0.009 7.44 0.050 1.01 0.0002 Variant 11% Zn ~A356 0.22 0.23 0.072 0.36 0.010 7.38 0.047 2.93 0.0002 Variant 23% Zn ~A356 0.30 0.21 0.064 0.44 0.009 7.41 0.041 2.96 0.0002 Variant 33% Zn Cu, Mn

EXAMPLE 2 Behavior of the Clad Sheet Aluminum Alloy Under BrazingConditions

An investigation of the behavior of the clad sheet aluminum alloy underbrazing conditions was conducted. “Variant 2” cladding alloy (Table 4)was tested. A conventional aluminum alloy AA4343+1 Zn modified with Srand clad on a X902 core alloy was used as a control. FIG. 12 shows themicrostructures of the “as cast” alloys being tested. Notably, “variant2” alloy did not contain Sr, which is used to modify the Si particles inthe as cast ingot from needle shape to fine spherical shape. As seen inpanel B, “as cast” “variant 2” alloy contained larger Si particles dueto the absence of Sr. Inclusion of Sr is not a requirement for acladding alloy to be suitable for brazing applications. However, furthertesting of commercial size casting of ingots is envisioned to ascertainwhether Sr or Na additions are desirable for commercial casting.

A comparison of the brazing sheets produced from each cladding alloy isshown in FIG. 13. Panel A of FIG. 13 shows a longitudinal section of acontrol clad sheet alloy. Panel B of FIG. 13 shows a longitudinalsection of variant 2 casting alloy. The micrographs shown in FIG. 13support a conclusion that the variant casting alloy exhibits amicrostructure similar to that of a standard cladding alloy. Although“variant 2” alloy did not contain Sr to modify the Si particles, theresulting microstructure was still relatively fine and well dispersed.The ingots used in the experiment were direct chill cast in a smallingot 3.75×9×24 inches. The solidification rate was higher than thattypically observed in a commercial ingot, which may be 6 feet wide by 24inches thick by 20 feet long. However, it is envisioned that thecladding alloys according to the embodiments of the present inventionwill produce a microstructure suitable for brazing applications whencast in commercial ingots.

FIG. 14 is a micrograph showing post braze comparison of the samplesshown in FIG. 13. The samples photographed for FIG. 14 were obtained byexposing the coupons of the sample clad alloys shown in FIG. 13 to 602°C.-606° C., then soaking them for 3 minutes, meaning that thetemperature was “held” between 602 and 606° C. followed by cooling to570° C. before extracting the samples from the furnace and cooling toroom temperature. Coupons were produced in the laboratory and exposed toa braze cycle while in a vertical orientation. Panel A shows amicrograph of a longitudinal section of conventional AA4343+1 Zn clad.Panel B shows a micrograph of a longitudinal section of variant 2cladding alloy clad on X902 core alloy. A longitudinal section meaningthat the plane of polish is parallel to the rolling direction and theview shown in the figure is the through thickness of the sheet.

The examination of the micrographs shown in FIG. 14 revealed that thatin both samples the cladding flowed similarly, and a similar level ofresidual filler metal was present on the surface post-brazing. In bothcases, a dense precipitate band formed in the core adjacent to theresidual filler surface layer. Accordingly, both the experimental alloyand the control alloy exhibited appropriate melting and flow to thebottom of a coupon when exposed in a vertical orientation. The resultsof the testing support a conclusion that alloys of the present inventioncan fill or join two components by capillary action during a brazecycle.

EXAMPLE 3 Behavior of the Clad Sheet Aluminum Alloy in “Angle on Coupon”Test

A test commonly referred to as the “Angle on Coupon” test is conductedon the alloys described in the previous example. A coupon of about 1.25″square is produced from each clad sheet aluminum alloy. A small piece ofbent AA1100 is placed on each coupon. The coupon and angle are fluxed bydipping in a slurry of 16% NOCOLOK™ (Solvay, Houston, USA) flux in watercontaining a surfactant or, in the alternative, the flux is mixed in100% isopropyl alcohol. Either fluxing method deposits about 2-6 g/m² offlux onto the surfaces of the angles and the coupons. The angles and thecoupons can be lifted on one end or the other by a small wire, asillustrated in FIG. 15, thus forming a gap that can be filled by thecladding alloy during brazing. The test is used to detect the ability ofthe clad sheet aluminum alloys being tested to fill a gap of varyingsize. The length of the resulting fillet is evaluated post braze. It isobserved that the filler metal fills the gaps completely up to the wire.This ability of the filler metal shows that the filler metal has theappropriate fluidity to be “pulled” by the capillary action thatdevelops between the two surfaces.

EXAMPLE 4 Corrosion Testing of Experimental Clad Sheet Alloys

All the alloys shown in Table 4 were made into clad sheet alloys andtested for corrosion resistance. Corrosion testing of experimental cladsheet alloys was conducted and showed that the cladding alloys variant1, variant 2 and variant 3 left more residual re-solidified filler alloyon the surface of the coupons, as compared with standard alloys clad onthe same core. This result indicated that the experimental claddingalloys variant 1, variant 2 and variant 3 were less anodic to the coreally than the standard cladding alloys. Accordingly, a clad sheet alloycomprising an experimental cladding, which exemplifies embodiments ofthe present invention, can resist corrosion at brazed joints better thanthe conventional alloy. Brazed objects fabricated from an experimentalalloy may last longer before failure at the brazed joints due tocorrosion, in comparison to the objects fabricated from conventionalclad sheet alloys.

All patents, publications and abstracts cited above are incorporatedherein by reference in their entirety. Different arrangements andcombinations of the elements and the features described herein arepossible. Similarly, some features and subcombinations are useful andmay be employed without reference to other features and subcombinations.Various embodiments of the invention have been described in fulfillmentof the various objectives of the invention. It should be recognized thatthese embodiments are merely illustrative of the principles of thepresent invention. Numerous modifications and adaptations thereof willbe readily apparent to those skilled in the art without departing fromthe spirit and scope of the present invention.

1. An aluminum material comprising an aluminum alloy core and analuminum alloy cladding, wherein the aluminum alloy cladding comprises≦1.0 wt % Cu, ≦0.5 wt % Fe, ≦1.0 wt % Mn, ≦15 wt % Si, ≦0.15 wt % Ti, ≦7wt % Zn and at least one of Sr or Na, remainder Al.
 2. The aluminummaterial of claim 1, wherein the aluminum alloy cladding comprises0.2-0.3 wt % Cu, 0.2-0.3 wt % Fe, ≦0.6 wt % Mn, 7-12 wt % Si, 0.05-0.15wt % Ti, 0-3.5 wt % Zn and at least one of Sr or Na, remainder Al. 3.The aluminum material of claim 1, wherein the aluminum alloy claddingcomprises 0.1-1.0 wt % Cu, 0.1-0.5 wt % Fe, ≦1.0 wt % Mn, 3-15 wt % Si,≦0.15 wt % Ti and ≦7 wt % Zn and at least one of Sr or Na, remainder Al.4. The aluminum material of claim 1, wherein the aluminum alloy claddingcomprises 0.15-0.6 wt % Cu, 0.1-0.4 wt % Fe, ≦0.7 wt % Mn, 5-12 wt % Si,0.01-0.15 wt % Ti and at least one of Sr or Na, remainder Al.
 5. Thealuminum material of claim 1, wherein the aluminum alloy claddingcomprises 0.15-0.3 wt % Cu, 0.2-0.4 wt % Fe, ≦0.5 wt % Mn, 7-12 wt % Si,≦0.13 wt % Ti, and at least one of Sr or Na, remainder Al.
 6. Thealuminum material of claim 1, wherein the aluminum alloy claddingcomprises ≦1.0 wt % Cu, ≦0.5 wt % Fe, ≦1.0 wt % Mn, ≦15 wt % Si, ≦0.15wt % Ti, ≦7 wt % Zn and 0.005-0.05 wt % Sr, remainder Al.
 7. Thealuminum material of claim 1, wherein the aluminum alloy claddingcomprises ≦1.0 wt % Cu, ≦0.5 wt % Fe, ≦1.0 wt % Mn, ≦15 wt % Si, ≦0.15wt % Ti, ≦7 wt % Zn, 0.01-0.025 wt % Sr and one or more of ≦0.2 wt % Mgor ≦0.05 wt % Ni, remainder Al.
 8. The aluminum material of claim 1,wherein the aluminum alloy cladding comprises ≦1.0 wt % Cu, ≦0.5 wt %Fe, ≦1.0 wt % Mn, ≦15 wt % Si, ≦0.15 wt % Ti, ≦7 wt % Zn, 0.01-0.025 wt% Sr, ≦0.2 wt % Mg and ≦0.05 wt % Ni, remainder Al.
 9. The aluminummaterial of claim 1, wherein the aluminum alloy cladding comprises0.2-0.3 wt % Cu, 0.2-0.3 wt % Fe, ≦0.6 wt % Mn, 7-12 wt % Si, 0.05-0.15wt % Ti, 0-3.5 wt % Zn, 0.01-0.025 wt % Sr, ≦0.1 wt % Mg and 0.005-0.02wt % Ni, remainder Al.
 10. The aluminum material of claim 1, wherein thematerial is in a form of a sheet comprising the aluminum alloy core andhaving the aluminum alloy cladding on one side of the sheet or on bothsides of the sheet.
 11. The aluminum material of claim 1, wherein thealuminum alloy core comprises a 3xxx or 6xxx series aluminum alloy. 12.A process for preparing the aluminum material of claim 1, comprising:casting the aluminum alloy cladding; rolling the aluminum alloy claddingto a required thickness, thus producing rolled aluminum alloy cladding;assembling the rolled aluminum alloy cladding onto at least one side ofthe rolled aluminum alloy core; and, hot roll bonding the rolledaluminum alloy cladding onto the rolled aluminum alloy core.
 13. Aprocess for preparing the aluminum material of claim 1, comprisingfusion casting the aluminum alloy core and the aluminum alloy cladding.14. The process of claim 11, further comprising preparing the aluminumalloy cladding prior to casting from scrap aluminum with addition of Sior from a combination of scrap aluminum and smelter grade aluminum. 15.A process comprising joining by brazing at least one first aluminumalloy form fabricated from the aluminum material of claim 1 with asecond aluminum alloy form.
 16. An object fabricated by a processcomprising the process of claim
 15. 17. The object of claim 16, whereinthe object is a heater, an evaporator plate, an evaporator, a radiator,a heater core, a condenser, a tube, a pipe or a manifold.
 18. A processof joining two or more aluminum forms by brazing, wherein at least oneof the two or more aluminum forms is fabricated from the aluminummaterial of claim 1, comprising: assembling and securing the two or morealuminum forms together; heating the two or more aluminum forms to abrazing temperature until joints are created among the two or morealuminum forms by capillary action; and, cooling the two or morealuminum forms below solidus of the aluminum alloy cladding.
 19. Theprocess of claim 18, wherein the brazing temperature is between 590° C.and 610° C.
 20. An object fabricated by a process comprising the processof claim
 18. 21. The object of claim 20, wherein the object is a heater,an evaporator plate, an evaporator, a radiator, a heater core, acondenser, a tube, a pipe or a manifold.